Playing subtitles not included on the disc

[Fixation]

I want to watch Ghost in the Shell Stand Alone Complex legitimately in 1080p, however the only released Blu-Rays of the entire series (S.A.C Trilogy features heavily condensed versions) are a set of 4 Japanese box set releases.

While they do have dual audio, they do not have English subtitles and I wish to watch GITS in Japanese with English subtitles.

Is there a way to watch these discs with external subtitles, or any other solution that allows me to watch from the original disc? I don't want to burn them to my SSD; I want the discs to be what I use because these box sets altogether are ~£400/$700.

As these are series BDs with multiple episodes, I'd also appreciate any tips on how to make the loading of subtitles for each episode as seamless/painless as possible.

Thanks in advance,

Fix